M.V. Hutz
aca197ef51
## Description `iterator.Try` previously copied the entire iterator and synced it back on success, causing an unnecessary heap allocation on every call. This PR simplifies `Try` to save and restore the index directly, and removes the now-unused `Copy` and `Sync` methods. - Rewrite `ScanRune` and `ParseRawToken` as peek-then-advance, eliminating the need for `Try` at leaf level. - Remove redundant `Try` wrappers from `parseExpression`, `parseAbstraction`, `parseApplication`, `parseLet`, and `parseToken`, which are already disambiguated by their callers. - Keep `Try` only where true backtracking is needed: `parseStatement`, which must choose between `parseLet` and `parseDeclare`. - Fix pre-existing panic in saccharine `parseExpression` when the iterator is exhausted (added `Done()` guard). ### Decisions - `Try` now operates on the original iterator instead of a copy, removing the confusing pattern where the callback's `i` was a different object than the caller's `i`. - Removed `parseSoftBreak` and `parseHardBreak` helper functions since `ParseRawToken` no longer needs `Try` wrapping. ## Benefits - Eliminates a heap allocation per `Try` call. - Reduces nesting and indirection in all parse functions. - Makes the code easier to follow by removing the shadow-`i` pattern. - `Try` is now only used at genuine choice points in the grammar. ## Checklist - [x] Code follows conventional commit format. - [x] Branch follows naming convention (`<type>/<description>`). Always use underscores. - [x] Tests pass (if applicable). - [x] Documentation updated (if applicable). Reviewed-on: #47 Co-authored-by: M.V. Hutz <git@maximhutz.me> Co-committed-by: M.V. Hutz <git@maximhutz.me>
96 lines
2.2 KiB
Go
96 lines
2.2 KiB
Go
// Package iterator defines a generic way to iterator over a slice of data.
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package iterator
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import "fmt"
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// An Iterator traverses over slices.
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type Iterator[T any] struct {
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items []T
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index int
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}
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// Of creates a new iterator, over a set of defined items.
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func Of[T any](items []T) *Iterator[T] {
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return &Iterator[T]{items: items, index: 0}
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}
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// Index returns the current position of the iterator.
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func (i Iterator[T]) Index() int {
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return i.index
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}
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// Get returns the datum at the current position of the iterator.
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func (i Iterator[T]) Get() (T, error) {
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var null T
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if i.Done() {
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return null, fmt.Errorf("iterator is exhausted")
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}
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return i.items[i.index], nil
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}
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// MustGet is a version of Get, that panics if the datum cannot be returned.
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func (i Iterator[T]) MustGet() T {
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t, err := i.Get()
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if err != nil {
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panic(fmt.Errorf("cannot get current token: %w", err))
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}
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return t
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}
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// Forward increments the iterator if the iterator is not yet at the end of the
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// slice.
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func (i *Iterator[T]) Forward() {
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if !i.Done() {
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i.index++
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}
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}
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// Next attempts to increment the iterator. Returns an error if it cannot be
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// incremented.
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func (i *Iterator[T]) Next() (T, error) {
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item, err := i.Get()
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if err == nil {
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i.index++
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}
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return item, err
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}
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// Back decrements the iterator. If the iterator is already at the beginning of
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// the slice, this is a no-op.
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func (i *Iterator[T]) Back() {
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i.index = max(i.index-1, 0)
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}
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// Done returns whether the iterator is at the end of the slice or not.
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func (i Iterator[T]) Done() bool {
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return i.index == len(i.items)
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}
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// While increments the iterator as long as the current item satisfies the
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// predicate. The first item that does not match is left unconsumed.
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func (i *Iterator[T]) While(fn func(T) bool) {
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for !i.Done() {
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if !fn(i.MustGet()) {
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return
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}
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i.Forward()
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}
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}
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// Try attempts to perform an operation using the iterator. If the operation
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// succeeds, the iterator keeps its new position. If the operation fails, the
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// iterator is rolled back, and an error is returned.
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func Try[T any, U any](i *Iterator[T], fn func(i *Iterator[T]) (U, error)) (U, error) {
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saved := i.index
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out, err := fn(i)
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if err != nil {
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i.index = saved
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}
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return out, err
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}
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